I have looked through my 300 F/2.8 with an eyepiece via an adapter bought from moggadapters.com.au
The view was rather good, extremely wide at 300mm, focusing done via the lens focusing ring.. (which was VERY fiddly)
I have also organised a M42 T thread to EF lens adapter, which you could then adapt an SCT type diagonal + ep.. which would also work...
As Dennis mentioned, the idea of L glass dripping in dew the way my telescopes sometimes do scares me a little... that being said, a dew heater on my 300mm's front element and on the rear was enough to keep the whole body of the lens warm enough to resist dew...
Bert's belt drive setup would be easy enough to duplicate, even with something as basic as the skywatcher electric focuser. take off the clamp that would normally go onto the focus knob shaft, put on a small pulley, run a rubber 'o' ring from the pulley to the focus ring of the lens.. tap a button to move focus in and out.... Futhermore you could then adapt it to run of a FCUSB from shoestring for computer control...
For imaging I think DSLR lenses are the goods with their very fast apertures, however for visual, it would be cheaper to buy an APO scope of the same size.
300mm F/2.8L 117mm front element = >$5000
400mm F/4L - ~129mm front element = >$5600
400mm F/2.8L "" >$8900
WO FLT132 ~$5000
EDIT : !!2000th Post!!
